Data Over Cable Service Interface Specification (DOCSIS) 3.0 technology with its multiple bonded channels is enabling new services such as Internet Protocol (IP) Video delivery over the larger DOCSIS 3.0 pipe. These video streams are typically delivered as multicast packets to a cable modem termination system (CMTS) and “switched” by the CMTS so that only those video streams being watched are actually sent down a DOCSIS channel. Today, Constant Bit Rate (CBR) video streams are typically used because of the simplified traffic management associated with them. Variable Bit Rate (VBR) video streams provide a significantly lower overall average bit rate than CBR (e.g., 30-40%), but it may have peak rates that are two to three times its average rate. If multiple VBR streams in a given channel peak simultaneously, the bandwidth required may exceed the capacity of the channel. Since the video streams might not be encoded jointly, this phenomenon is non-deterministic and may result in dropped packets. With the extensive encoding used in video streams today, each dropped packet can introduce significant impairments to the video quality. If the channel congestion causes the Customer Premises Equipment (CPE) video buffers to underflow, some decoders have been known to lock and require a reset. With today's high-definition services, quality is an extremely important feature so dropped packets are a significant issue.
Today, VBR is often used for broadcast video services where a Statistical Multiplexer can rate shape the peaks as needed to keep the bandwidth within the channel capacity and prevent dropped packets. However, the complexity of Statistical Multiplexers makes them economically unfeasible to use for extensive narrowcast services with smaller service groups expected in IP Video systems.
Some IP Video delivery systems have packet recovery algorithms. These could potentially be used to recover packets that are dropped when the channel capacity is exceeded. The drawbacks of this approach are the added costs of the repair servers and added buffer delays needed to account for the detection, request and re-transmission of dropped packets. Another common packet recovery method is to provide packet level forward error correction (FEC) that the CPE client can use to recover dropped packets. The drawbacks of this approach are the 5% to 20% additional channel capacity required to send the FEC and the extra processing power required by the CPE.
A problem is caused by current bonding limitations with DOCSIS 3.0 devices. For example, to scale IP Video to service groups of several hundred subscribers could require a total 16 to 24 channels for IP Video, which exceeds the abilities of today's commercially available cable modems and cannot be bonded into a single bonding group. Today's commercially available cable modems support only the minimum DOCSIS 3.0 required 4 bonded channels; and even next generation modems about to come to market provide a maximum of 8 bonded channels, some of which are needed for high speed data service, instead of IP Video. Dividing 16 to 24 IP video channels into smaller 4-8 channel bonding groups reduces the overall statistical advantages gained and increases the total number of channels needed. At the same time, choosing a fixed sized bonding group (e.g., 4 bonded channels) for the IP Video service excludes any other devices that may, for example, only have 1, 2 or 3 channels available for the IP Video service.
The prior art in Ramakrishnan, “Scaling the DOCSIS Network for IPTV,” SCTE ET 2009 (hereinafter referred to as “Ramakrishnan”), discloses a packing efficiency improvement provided by 4-channel bonding. FIG. 1A and FIG. 1B depict an illustrative comparison of 4 separate quadrature amplitude modulation (QAM) channels to a 4-channel bonding group, in accordance with the prior art. In one embodiment, the QAM channels are 6-MHz North American signals. FIG. 1A shows 4 separate (and unbonded) QAM channels (QAM1-QAM4) having a channel capacity that allow 10 unbonded standard-definition (SD) streams (SD1-SD10) and 5 unbonded high-definition (HD) streams (HD1-HD5), but leaving QAM channel capacity that is not used because it is not sufficient to allow any additional unbonded HD streams. FIG. 1B shows 4 bonded QAM channels (QAM1-QAM4) having a channel capacity that allow 10 bonded SD streams (SD1-SD10) and 7 bonded HD streams (HD1-HD7). Thus, 4 bonded QAM channels can provide more video capacity than 4 separate (and unbonded) QAM channels.
The prior art in Bernstein & Liu, “VBR Video Services in DOCSIS 3.0 Networks,” NCTA 2008 (hereinafter referred to as “Bernstein”) reach a similar conclusion to Ramakrishnan. Bernstein discloses that VBR in a 4-channel bonding group provided a 57.5% increase (i.e., 63 streams for 4 channels); while VBR in a single unbonded channel provided a 40% increase (i.e., 14 streams for a single channel, or 56 streams across 4 single channels). For example, in Bernstein, FIG. 4 illustrates VBR network statistical multiplexing bandwidth utilization improvement. Hence, Bernstein discloses that bonding 4 channels together can provide an increase in video capacity from 56 to 63 streams. The problem now is that all devices wishing to see these video services must support 4 bonded channels. All other devices cannot access this content.
There is a demand for an IP video delivery method and system to allocate flexibly sized bonding group over unbonded channels. The presently disclosed invention satisfies this demand.